    /** 
    * 
    *  Base64 encode / decode 
    * 
    *  @author haitao.tu 
    *  @date   2010-04-26 
    *  @email  tuhaitao@foxmail.com 
    * 
    */  
       
    function Base64() {  
       
        // private property  
        _keyStr = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";  
       
        // public method for encoding  
        this.encode = function (input) {  
            var output = "";  
            var chr1, chr2, chr3, enc1, enc2, enc3, enc4;  
            var i = 0;  
            input = _utf8_encode(input);  
            while (i < input.length) {  
                chr1 = input.charCodeAt(i++);  
                chr2 = input.charCodeAt(i++);  
                chr3 = input.charCodeAt(i++);  
                enc1 = chr1 >> 2;  
                enc2 = ((chr1 & 3) << 4) | (chr2 >> 4);  
                enc3 = ((chr2 & 15) << 2) | (chr3 >> 6);  
                enc4 = chr3 & 63;  
                if (isNaN(chr2)) {  
                    enc3 = enc4 = 64;  
                } else if (isNaN(chr3)) {  
                    enc4 = 64;  
                }  
                output = output +  
                _keyStr.charAt(enc1) + _keyStr.charAt(enc2) +  
                _keyStr.charAt(enc3) + _keyStr.charAt(enc4);  
            }  
            return output;  
        }  
       
        // public method for decoding  
        this.decode = function (input) {  
            var output = "";  
            var chr1, chr2, chr3;  
            var enc1, enc2, enc3, enc4;  
            var i = 0;  
            input = input.replace(/[^A-Za-z0-9\+\/\=]/g, "");  
            while (i < input.length) {  
                enc1 = _keyStr.indexOf(input.charAt(i++));  
                enc2 = _keyStr.indexOf(input.charAt(i++));  
                enc3 = _keyStr.indexOf(input.charAt(i++));  
                enc4 = _keyStr.indexOf(input.charAt(i++));  
                chr1 = (enc1 << 2) | (enc2 >> 4);  
                chr2 = ((enc2 & 15) << 4) | (enc3 >> 2);  
                chr3 = ((enc3 & 3) << 6) | enc4;  
                output = output + String.fromCharCode(chr1);  
                if (enc3 != 64) {  
                    output = output + String.fromCharCode(chr2);  
                }  
                if (enc4 != 64) {  
                    output = output + String.fromCharCode(chr3);  
                }  
            }  
            output = _utf8_decode(output);  
            return output;  
        }  
       
        // private method for UTF-8 encoding  
        _utf8_encode = function (string) {  
            string = string.replace(/\r\n/g,"\n");  
            var utftext = "";  
            for (var n = 0; n < string.length; n++) {  
                var c = string.charCodeAt(n);  
                if (c < 128) {  
                    utftext += String.fromCharCode(c);  
                } else if((c > 127) && (c < 2048)) {  
                    utftext += String.fromCharCode((c >> 6) | 192);  
                    utftext += String.fromCharCode((c & 63) | 128);  
                } else {  
                    utftext += String.fromCharCode((c >> 12) | 224);  
                    utftext += String.fromCharCode(((c >> 6) & 63) | 128);  
                    utftext += String.fromCharCode((c & 63) | 128);  
                }  
       
            }  
            return utftext;  
        }  
       
        // private method for UTF-8 decoding  
        _utf8_decode = function (utftext) {  
            var string = "";  
            var i = 0;  
            var c = c1 = c2 = 0;  
            while ( i < utftext.length ) {  
                c = utftext.charCodeAt(i);  
                if (c < 128) {  
                    string += String.fromCharCode(c);  
                    i++;  
                } else if((c > 191) && (c < 224)) {  
                    c2 = utftext.charCodeAt(i+1);  
                    string += String.fromCharCode(((c & 31) << 6) | (c2 & 63));  
                    i += 2;  
                } else {  
                    c2 = utftext.charCodeAt(i+1);  
                    c3 = utftext.charCodeAt(i+2);  
                    string += String.fromCharCode(((c & 15) << 12) | ((c2 & 63) << 6) | (c3 & 63));  
                    i += 3;  
                }  
            }  
            return string;  
        }  
    }  